U.S. Immigration and Customs Enforcement says it has acquired new space in federal prisons to house immigrant detainees — more than 1,600 beds.Because of a "current surge in illegal border crossings" and the Trump administration's "zero-tolerance policy," ICE entered into agreements with the Federal Bureau of Prisons (BOP), the agency said Thursday."The use of BOP facilities is intended to be a temporary measure until ICE can obtain additional long-term contracts for new detention facilities or until the surge in illegal border crossings subsides," ICE spokesperson Danielle Bennett said in a statement emailed to NPR.A facility in Victorville, Calif., will house the most detainees — 1,000 — while locations in Seattle; La Tuna, Texas; Sheridan, Ore.; and Phoenix will hold between 102 and 230 detainees.A former ICE official under the Obama administration, Kevin Landy, called the move "highly unusual," telling Reuters that a "large percent of ICE detainees have no criminal record and are more vulnerable in a prison setting."Earlier this week, the Department of Homeland Security released new figures showing an increase in arrests of people attempting to cross the southern U.S. border illegally — almost 52,000 people were arrested in May, the agency said. That's a sharp increase from May 2017, when that number was just under 20,000.U.S. Attorney General Jeff Sessions announced a new "zero-tolerance" policy in April, saying the government would prosecute anyone attempting to enter the country unlawfully.Sessions also said last month that the government would separate migrant parents from their children, leading to an outcry among immigrant advocates after at least 600 children were separated from their parents in one month."If you don't like that, then don't smuggle children over our border," Sessions said.On Wednesday, a federal judge allowed a lawsuit against the Trump administration's separation policy to proceed, saying, "Such conduct, if true, is brutal, offensive, and fails to comport with traditional notions of fair play and decency," as NPR's Joel Rose reported.Under the Obama administration, immigrants who were arrested "without serious criminal records were allowed to await their court dates while living in the United States," Reuters notes. "Others were housed in immigration detention facilities or local jails."The Department of Homeland Security and the Justice Department released a report Thursday saying that 57,820 "known or suspected aliens" were in the custody of the DOJ at the end of the first quarter of the 2018 fiscal year. The Bureau of Prisons is a part of the DOJ. Copyright 2018 NPR. To see more, visit http://www.npr.org/.